Scanning Polarization Lidar LOSA-M3: Opportunity for Research of Crystalline Particle Orientation in the Clouds of Upper Layers

Abstract. The article describes a scanning polarization lidar LOSA-M3, developed at the Institute of Atmospheric Optics, the Siberian Branch of Russian Academy of Sciences (IAO SB RAS). The first results of studying the crystalline particles orientation by means of this lidar are presented herein. The main features of LOSA-M3 lidar are the following: 1) an automatic scanning device, which allows to change the sounding direction in the upper hemisphere at the speed up to 1.5 degrees per second with the accuracy of angle measurement setting at least 1 arc minute; 2) separation of polarization components of the received radiation is carried out directly behind the receiving telescope, without installing the elements distorting polarization, such as dichroic mirrors and beamsplitters; and 3) continuous alternation of the initial polarization state (linear - circular) from pulse to pulse that makes it possible to evaluate some elements of the scattering matrix. Several series of measurements of the ice cloud structure of the upper layers in the zenith scan mode were carried out in Tomsk in April-October 2018. The results show that the degree of horizontal orientation of particles can vary significantly in different parts of the cloud. The dependence of signal intensity on the tilt angle reflects the distribution of particle deflection relative to the horizontal plane, and is well described by the exponential dependence. The values of cross-polarized component in most cases show a weak decline of intensity with the angle. However, these variations are smaller than the measurement errors. We can conclude that it is practically independent of the tilt angle. In most cases the scattering intensity at the wavelength of 532 nm has a wider distribution than at 1064 nm.